1. Field of the Invention
The present invention relates to materials testing and, more particularly, to bio-medical and bio-materials testing and motion studies of cadaveric spinal specimens, functional spinal units (FSU), simulated spine models and spinal constructs. Though the primary application is for spine testing, the present invention may also be useful in testing other biological units for which unconstrained physiological loading is important, including, but not limited to, ankles, knees, wrists, feet, and hands.
2. Description of Related Art
The field of materials testing related to biomaterials and biomedical products has seen significant growth in recent years. Current materials test systems employed in the field of spinal research have become extremely complex and expensive.
Typical specimens or articles to be tested include cadaveric spines or sections thereof; an FSU; simulated spine models; or spinal constructs. The most basic specimen would typically be a cadaveric spine or simulated FSU as shown in FIG. 1.
An FSU is also known as a single motion segment of the spine which is the smallest physiological motion segment to exhibit similar biomechanical characteristics to those of the entire spine. An FSU includes two adjacent vertebrae (100) and the intervertebral disc (101) along with all of the adjoining ligaments between them (not shown in FIG. 1 for clarity). The FSU would exclude all of the connecting musculature. The vertebrae have anterior and posterior surfaces. The posterior surface is identified by the central location of the spinous process (not shown) and the transverse process (102) which extends laterally from the posterior half of the vertebra. FIG. 1 shows the three anatomical axes, X, Y, and Z, which converge at the vertebra. The X axis represents the horizontal axis about which lateral bending occurs, the Y axis represents the horizontal axis about which flexion and extension occurs, and the Z axis represents the vertical axis about which axial rotation occurs. The FSU shown in FIG. 1 is capable of six degrees of freedom, namely, translation along each of the axes (X, Y, and Z) and rotation about each of those axes.
A majority of currently available commercial and non-commercial automated test systems used for spinal testing attach to the top of the specimen and affix the bottom of the specimen through the use of some type of attachment point or clamping mechanism. Through the use of multiple motors and computer control systems, the test systems attempt to replicate in vivo motion. While some complex test systems may come close to achieving this goal, most do not because they produce motion through constrained attachment and programmed control which “moves the spine where the machine wants to move it”.